LeetCode 206. 反转链表

题目链接

206. 反转链表

思路分析

迭代

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        if(!head || !head->next) return head;
        auto a = head, b = a->next;
        while(b){
            auto c = b->next;
            b->next = a;
            a = b, b = c;
        }
        head->next = NULL;
        return a;
    }
};

递归

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        if(!head || !head->next) return head;
        auto tail = reverseList(head->next);
        head->next->next = head;
        head->next = NULL;
        return tail;
    }
};